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1974 R90/6 Engine Chirp

Hi folks, I?ve got a nice-running 74 R90/6 that makes an engine chirp
I do not have another airhead to compare this to, but it does not seem normal.
This bike has done this as long as I have owned it (about 2 years) and only when it is warmed up. When the bike is warm, it chirps, and the sound persists for as long as you ride it.
The noise is most obvious (easiest to hear) at idle, especially right as you kill the engine. It will do this in gear and in neutral.
The bike has about 40,000 miles (but not sure if the odo is accurate for actual miles on the bike). Engine has BMW 20/50, and I live in Texas.
I made a video of the sound this morning. Bike was idling, I revved the engine, then let it idle and killed it.
Anybody seen something like this?
Any advice on whether or not to do something about it?
Thanks so much

I have heard in the past that the tube (or the little valve that feeds the tube) that returns oil spray from the crankcase into the right carb can chirp. I have a /6 and it hasn't chirped, but I believe there was a kit you could get for this condition. Otherwise, the bike runs fine, right?

I have a hard time defining what a "chirp" is; but there is a bird like sound that some have called the turkey gobble. Yes, this is the reed valve that allows the engine to "breathe" vapors from the crankcase/engine and dump it into the right carb. The fix is an upgrade of new reed valve. A pretty simple fix that requires one to pull the tank, remove the starter cover, pull the valve, install the new one correctly (there are a couple of tricks here), and reassemble. You might do a search for this or perhaps Kurt will chime in with his valuable pages and references.......God bless.......Dennis

Joe, thanks, and yes, the bike runs great.
I was wondering if this was something I should address, or if it is just one of those things some airheads will do.
Any idea on where to find one of these kits? Or if there is a name for the kit?

Dennis, I just saw your post and thanks for the good info.
That sounds like a reasonable fix. I will start some research on the parts and process, and would appreciate anyone other input on getting it done.
Thanks!
In the meantime, here is a photo of the bike this morning

I had a hard time hearing any kind of chirping. If not the engine breather valve, then if the engine is overfull of oil, it will create high internal pressure when the cylinders get to BTDC which can then create problems with seals, such as the rear main seal.

R90/6 chirp

After 35k miles, my 1974 R90/6 started to chirp and it got very loud, only at idle and slow speeds. BMW of Marin said that the spring that holds the flapper valve, my term, gets weak and it doesn't open straight up and down. They installed the fix it kit and no more chirp. Over filling the oil will also cause more back pressure and may be the cause. Just my experience, my R90/S never had a chirp. Current 1976 R90/6 30k miles, just purchased in February, does not chirp. Will update as the miles increase.

1974????

Drilled brake roters did not appear until 1975. 1974 models still had a kickstarter.

I'm thinking that you own a 1975 R90, not a '74.

There are a few other differences (frame gusseting, transmission internals, etc.), which might come into play when acquiring parts for your bike.
You might want to double check your bike actual birthdate via a VIN information locator (Snowbum's site?).

Wow, thanks so much everyone!
The advice and links are a tremendous help
On the year, I glanced at the frame tag and it read 1974, so maybe the bike is a mix or maybe BMW year models did not follow the typical calendar (like the Pentons I have)
Anyway, many thanks!

BMW should have kept up their typically models where bikes built in August of a given year are that year models; bikes built in September of a given year are the next year's models. The other general thing is that the factories would shut down for August in order to retool for the next model year. That said, there is much conjecture that on the cusp of a year changeover, whatever is in the parts bin gets used on the production line. So there could be some unusual configuration on bikes built in August or September.